Abstract

The principal efferent role of the macrophage in acquired resistance to intracellular pathogens depends on activation of T-cell lymphokines, primarily gamma interferon (IFN-γ). However, mouse macrophages that are heavily burdened with Mycobacterium leprae are refractory to activation by IFN-γ and are thus severely compromised in their capacity for both enhanced microbicidal and tumoricidal activities. We report here that lipoarabinomannan (LAM), a highly immunogenic lipopolysaccharide that is a prominent component of the cell walls of M. leprae and M. tuberculosis, was a potent inhibitor of IFN-γ-mediated activation of mouse macrophages in vitro. Inhibition of macrophage activation by LAM required preincubation for approximately 24 h, resulting in uptake of LAM into cytoplasmic vacuoles of macrophages. Intact LAM was necessary to inhibit IFN-γ-mediated activation, as this property was lost when the acyl side chains were removed from LAM by mild alkaline hydrolysis. In addition, LAM was an abundant constituent of macrophages isolated from lepromatous granulomas of M. leprae-infected nude mice and likely contributed to the defective activation of granuloma macrophages by IFN-γ.

Original languageEnglish
Pages (from-to)1232-1236
Number of pages5
JournalInfection and immunity
Volume56
Issue number5
StatePublished - 1988

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